Groton — City and Naval Submarine Base firefighters on Monday morning spent about half an hour working to extinguish a fire in the engine of a rock-crushing construction vehicle.

According to Groton City Fire Chief Nick Delia, the call for the fire near the sub base’s main gate came in at 10:42 a.m.

Delia said crews learned not long after arriving that the operator of the truck, in an attempt to help, had dumped dirt on the engine. Once firefighters removed the dirt, they then used foam to stop the blaze.

Because of the heat — Monday’s high approached 90 degrees — city and sub base firefighters were rotated more frequently than usual, Delia said.

Delia said the cause of the fire likely will be undetermined because the engine was quite burnt. He said the motor will need a substantial amount of work if the operator wants to run the vehicle again.

Military Highway was closed in the area for about an hour.